It could be a challenger if it does something like the early days of Reddit, aggregating content and attracting more users. It could do with a couple of UI tweaks and probably a Android app too. So, Mr.Jimmy Wales, are you looking for developers? Because we could try creating an awesome online community for building this as open-source.
I do hope the ad-targetting social networks do reduce, and community funded ones can raise up and take over the market.